Starfield: Who is The Emissary?

There are plenty of interesting characters in Starfield, but none more so than The Hunter and The Emissary. The former first comes across as some cold-hearted killer, while the latter is portrayed as someone who wants to protect the mysteries of the universe from those who are unworthy of unearthing them. However, the more time that Starfield players spend in their company, the more it becomes clear that there is a lot more to the pair than first meets the eye.